Both rising stem and nonrising stem through conduit gate valves are utilized in industry to control the flow of fluids in flow passages such as in land-based and subsea oil and gas wells and in petroleum and petrochemical pipelines. A common concern of both gate valve types is to provide an effective seal in a gate valve flow passage for the entire set of pressure differentials encountered during various fluid transportation and industrial operations. Various structural approaches have been made to effect a better seal when high pressure differentials (&gt;5000 psi) are encountered and to alleviate problems opening and closing the gate valve during high-pressure operations.
U.S. Pat. No. 3,269,694, issued to Hardison, introduces the use of a pressure-balance shaft and lever-type gate valve to address the problem of shaft binding when the valve is opened and closed during high-pressure operations. It also provides a means for preventing spring-biased, floating, or pressure-actuated seals from moving into the path of the gate and thus being damaged during valve opening and closing.
U.S. Pat. No. 4,376,524, issued to Shelton, addressed the need to alleviate the high thrust and torque requirements for gate members in nonrising stem gate valves during opening and closing when such gate members were subjected to high pressures (&gt;5000 psi). Thus, it introduced a low-stress connection in utilizing a series of extensions and collars to reduce the possibility of stress-produced hydrogen embrittlement and hydrogen corrosion cracking of the gate member.
U.S. Pat. No. 4,510,960 illustrates a gate secured to a stem by use of a nut secured rigidly to a threaded stem. U.S. Pat. No. 3,387,819 discloses a gate valve body construction which includes reinforcing members. U.S. Pat. No. 2,596,817 discloses a gate valve where the stem is connected through the gate by a slot in the gate. The gate bottom is also truncated. U.S. Pat. No. 2,793,002 discloses a threaded stem connected to a gate, as does U.S. Pat. No. 4,711,262. U.S. Pat. No. 4,377,273 discloses a rigid connection between the gate and the stem. U.S. Pat. No. 4,230,299 discloses a stem pinned to the gate. U.S. Pat. No. 3,188,049 indicates a gate having a slot to accommodate a projection on the stem to secure the stem to the gate. The NL Shaffer Co. type V gate valve, as indicated in its 1982 and 1983 catalog, included a gate having a T-shaped slot therethrough, a stem with a T-shaped nut threadedly secured to it, adapted for slidable mounting in the slot in the gate for lifting the gate up and down. U.S. Pat. No. 243,846 shows a threaded stem connected to a gate
However, during certain operations, such as gas injection operations performed during secondary or enhanced oil recovery, the pressure differentials encountered can be very low (&lt;100 psi), and a requirement exists to provide an effective seal at these low pressures which will provide an instantaneous dynamic response to the pressure transients experienced during these operations.
A situation often encountered when a perfect gas-tight seal is not maintained between the gate and its seat is that operators, in an attempt to effect a perfect seal, overtighten the handle and strip the stem and handle threads. This damage is prevented by utilizing the spring-energized, full floating, parallel gate/seat design which does not require a wedging force to effect a gas-tight seal.
A further common concern of all gate valves is their efficient manufacture at an industrial performance level. Thus, it is the general object of this invention to provide a more effective and more efficient low- and high-pressure gas-tight seal between the gate and its seat in gate valves such as those typically used in gas injection operations in secondary and enhanced oil recovery.
It is a further object of this invention to provide such an improved seal at lower production costs while maintaining a modularity in the design to allow for a complete replacement of the transmission assembly (stem and nut) without removing the gate from the body/seat assembly.